This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2002-97046, filed on Mar. 29, 2002: the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photo detect element and an optical semiconductor device and, more particularly, to an optical semiconductor device that is used in so-called visual sensitivity and luminous intensity measurement etc. for measuring luminous intensity by sensing visible light only.
2. Description of Related Art
In recent years, in optical semiconductor devices that are used for visual sensitivity and luminous intensity measurement, a single chipped photo detect element comprising photo diodes (hereafter, referred to as PD) and an amplifying operation processing circuit to perform the amplification and processing of optical signals from PD are used. As shown in FIG. 1, an n-type region 2 is formed on the surface of a p-type silicon substrate 1 and a p-type region 3 is formed on the surface of this n-type region 2. At two PN junctions formed in the vertical direction, two PD (PD14, PD25) are formed.
An optical absorption rate on Si wafer varies depending on a depth from the surface and this optical absorption depth dependency differs depending on a wavelength, as shown FIG. 9. As the distances of above-mentioned two PN junctions from the surface of the substrate are different, the spectral response characteristic differs for each PD, for example, as shown in FIG. 3. The photodiode PD1 has the maximum sensitivity at around a wavelength 600 nm and the photodiode PD2 at the position deeper than the photodiode PD1 has the maximum sensitivity at around a wavelength 900 nm in FIG. 3.
Thus, a predetermined sensibility; that is, visual sensitivity can be obtained by a photo detect element by processing outputs from the diodes PD1 and PD2 that have different spectral response characteristics through the amplifying operation processing circuit. The luminous intensity corresponding to the spectral luminous efficiency is measured by eliminating the infrared component of the output of the photodiode PD1 using the infrared component of the output of the PD2.
A photo detect element 10 having such characteristic as this is mounted on a glass epoxy resin (hereinafter referred to as Glass-Epoxy) made substrate and the like, cured and bonded thereon, as shown in FIGS. 10A-10D, and FIG. 11. After bonding the terminals of the photo detect element with gold wires, an enclosure is formed and separated after transfer molded by a transparent epoxy resin 14 in order to protect the photo detect element 10. Then, the photo detect element 10 is connected to an external circuit in a metallized portion 16.
In such the optical semiconductor device, carriers are generated by infrared ray incoming from the side of the photo semiconductor unit and a dicing face of the photo detect element, infrared ray near 1000 nm turned around in the photo detect element. As a result, the photo detect element gets a sub-peak of unnecessary infrared component of 900-1200 nm (centering around 1000 nm) in addition to a peak of visual sensitivity (550 nm) as shown in FIG. 8. That is, as a conventional optical semiconductor device detects unnecessary infrared component, the illumination intensity corresponding to spectral luminance efficiency could not be made.
That is, as an optical semiconductor device used for detecting spectral luminance efficiency, a defect is produced as a peak is detected in the infrared region. For example, when two light sources are set at the same luminous intensity, there is originally no difference in optical output current values and a light source ratio (A light source/fluorescent lamp) is one time. However, an optical semiconductor device having a characteristic to sense a sub-peak of a visual sensitivity in the above-mentioned infrared region senses the infrared region and when components of the infrared region of A light source are sensed, an output current value increases and a light source ratio becomes worse. Further, when flat and reflective materials (for example, white glass epoxy resin plate, etc.) are used for a substrate to install a photo detect element, the infrared component region is also reflected by the reflection of light from the substrate and the light source ratio is made further worse.
As explained in the above, a conventional optical semiconductor device has a sensing character in the infrared region and therefore, there was such a problem that the output also depends on infrared ray when a optical semiconductor device is used for visual sensing of luminous intensity.
Therefore, an object of the present invention is to provide an optical semiconductor device with its spectral sensitivity characteristic controlled more precisely by suppressing the sensitivity in an infrared region with such a defect of a conventional optical semiconductor device removed.
The optical semiconductor device of the present invention is characterized in that an n-type region is formed on a p-type substrate, a p-type region is formed on the surface of this n-type region, a photo detect element equipped with a first photo diode having peak wavelength sensitivity in a visible spectral region is provided on the interface between the n-type region and the p-type region, a second photo diode having peak wavelength sensitivity in the infrared region is provided on the interface between the p-type substrate and the n-type region, and specific resistance R of the p-type substrate is 1xe2x89xa6Rxe2x89xa63(xcexa9cm).